The objective of the work proposed is development of spin-label, cross-linking reagents which will provide information about the relative geometry and motions of the protein and glycoprotein components of mammalian cell membranes. The goal of the studies is detailed information about the arrangement of cell-surface receptors on normal and malignant forms of mammalian cells. The methods of carrying out this work are to be: (1) synthesize a new class of spin labels (lipophilic, bifunctional spin labels) from a few synthetic precursors; (2) in order to define conditions for application of the labels to membranes, to apply the new reagents to a membrane of simple composition, the sarcoplasmic reticulum; (3) to use the reagents to determine the proximity of the major glycoprotein of the red blood cell to other membrane components (a) on the outside and (b) on the inside of the membrane; (4) to apply the techniques developed above to normal and malignant cells.